One disadvantage of previous catheters is that during infusion of a liquid substance into a target tissue, the liquid substance may flow back along the outer wall of the catheter due to a pressure of the liquid in an administering region between the outer wall of the catheter and the adjacent body tissue. This backward flow in the space or gap between the outer wall of the catheter and the body tissue at a distal end of the catheter (the end that is inserted into the patient) is also referred to as backflow. When such backflow is present, computer-assisted simulation of a dispersion of the liquid in the adjacent brain tissue can be inaccurate. In such a simulation, the distal end of the catheter is ordinarily modelled as a point source. In reality, rather than a point source, the liquid substance is dispersed along the catheter in an indeterminable way.
The liquid substance may also exit the brain tissue through the space or gap between the catheter's outer wall and the body tissue. Exiting through this gap is possible when the distal end of the catheter is placed near an outer cerebral membrane without adequate sealing or if it is crossing a sulci. The escape of the liquid substance may adversely affect treatment. A seal may be attached to the outer wall of the catheter, however, such a seal may be obstructive or even damaging to the tissue while the catheter is inserted into the patient. An injury from the seal (rigid or otherwise) also could cause channels in the brain tissue. The liquid substance intended to be administered for treatment may escape from the administering region through these channels. Thus, when compared to the simulated dispersion that assumes a point source for the administered substance, the actual substance dispersions in the patient may have an undesirable deviation. For the simulation to match the treatment, it is advantageous to limit the backflow to a minimum. This also may allow the surgeon greater freedom in trajectory planning.
US Publication No. 2006/0116636 A1 discloses a catheter in which the distal end includes a coating that increases the catheter's volume in the presence of a liquid. This “swelling” may be used to create a seal between an outer wall of the catheter and the adjacent brain tissue. In a swelled state, however, the affected region of said catheter exhibits a smooth outer wall. Because the brain tissue is irregular in structure and the swollen region of the catheter has a smooth outer wall, the liquid to be administered may penetrate through fine channels between the swollen region and the brain tissue. Such liquid may flow past the seal towards the proximal end (handle end) of the catheter.